The present invention relates to tools used by plumbers in residential and commercial building construction, and more particularly, to a device which may be inserted into a waste pipe in order to seal the pipe for pressure testing.
Drain/waste/vent (DWV) pipe and fittings made of acrylonitrile butadiene styrene (ABS) (Trademark) or polyvinyl chloride (PVC) plastic are extensively utilized in the construction of sewer systems in both residential and commercial construction. In some locations, cast iron pipe, copper pipe or clay pipe are used in constructing drain, waste or vent pipes in commercial and residential structures. Most municipalities have a plumbing code, such as the Uniform Plumbing Code (UPC) , which requires that the sewer system in a residence or commercial building be capable of withstanding a predetermined internal pressure, typically between about five pounds per square inch and fifteen pounds per square inch, without any apparent leaks. In order to accomplish such a pressure test, it is necessary for each waste pipe to be sealed.
There have been several approaches for sealing waste pipes in order to accomplish a pressure test. One approach requires the insertion of an elastomeric plug into the waste pipe which is inflated against the walls of the pipe to effect a seal. See for example U.S. Pat. No. 4,614,206 of Mathison et al. These inflatable plugs are expensive and the inflation thereof is both time consuming and dangerous. Over-inflation can lead to explosions, which can injure the plumber.
An alternate approach is to glue a seal over the end of the waste pipe. The seal must later be broken out or a segment of the pipe cut off. This approach is expensive and time consuming. Frequently the broken out seal lodges in the waste pipe, causing plugging.
Yet another approach to sealing a waste pipe is to utilize a type of mechanical plug called a "dollar plug". See for example U.S. Pat. No. 4,493,344 of Mathison et al. This plug has a large wing nut which is turned by the plumber in order to squeeze an elastomeric O-ring member between plate members. The O-ring member is expanded against the internal walls of the waste pipe. These dollar plugs provide an unreliable seal, and are time consuming to install and remove. Also, repeated use of dollar plugs is sometimes impaired because they rust and become encrusted with grout and other debris.
U.S. Pat. No. 4,817,671 of Mathison et al. discloses a high pressure mechanical plug that uses a combination of an expanded elastomeric O-ring and circumferential gripping pins to seal a pipe. An open-ended hollow cylindrical body encloses a piston structure having a lower end wall and frustoconical ram. A draw bolt extends axially from the piston structure through an unthreaded hole in a top end plate connected to the cylindrical body. A nut threaded on this bolt is tightened to pull the piston structure upwardly into the cylindrical body, thereby squeezing the O-ring between the piston structure and a tapered lower end of the cylindrical body. The O-ring is expanded radially outwardly against the inner wall of the pipe to provide a fluid-impervious seal. At the same time, circumferentially spaced locking pins are engaged by the sloping wall of the frustoconical ram and pushed radially outward into gripping engagement with the inner wall of the pipe. This plug is specifically designed so that even after the nut is tightened, high pressure gas or water inside the pipe pushes against the lower end of the piston structure to further move the same upwardly. This further squeezes the O-ring and further moves the pins radially outwardly in order to "further secure" the plug in the pipe.
The plug of the aforementioned U.S. Pat. No. 4,817,671 of Mathison et al. has several disadvantages. The mechanical structure of this plug has many complex metal parts which are expensive to fabricate and assemble. These metal parts are subject to corrosion. Furthermore, when testing a large diameter plastic or clay pipe, e.g. a pipe having a diameter of six inches or more, the pins can push radially outwardly with enough force to fracture the pipe. This is because the piston structure is capable of unrestricted free upward movement toward the cylindrical body. After the nut is tightened, high fluid pressures within the pipe can urge the piston structure upwardly with sufficient axial force such that the resulting radial force on the pins exceeds the strength of the pipe.